This invention relates to a photographic support, and more particularly to a photographic support having an undercoating layer on a substrate (or base sheet) coated with a resin on both sides.
In recent years, as a photographic support, there has been used paper coated with a resin such as a polyolefin resin on both sides thereof. But since surfaces of such a water resistant photographic support are hydrophobic, it is difficult to strongly adhere a photographic emulsion layer using gelatin as a binder to the photographic support. Thus, such a hydrophobic surface of the resin such as a polyolefin is subjected to an activating treatment such as a corona discharge treatment, flame treatment, chemical treatment or the like, followed by coating with a photographic emulsion. But according to this method, since the activity of the thus activated resin surface is lowered with the lapse of time, the adhesion of the photographic emulsion layer becomes poor. Further, non-uniform static charge on the resin surface often causes non-uniform emulsion coating.
In order to improve photographic properties such as prevention of deterioration of activating treatment effect with the lapse of time, improvement of coating unevenness, and the like, it is proposed to form a hydrophilic colloid film, that is an undercoating layer, on the surface of a resin such as polyolefin immediately after the activation treatment (e.g. Japanese Patent Unexamined Publication (Laid-Open) No. 62-30244). In this reference, there have been disclosed various techniques for improving coating properties such as coatability and mottle inprovement and adhesive properties of the undercoating layer and the photographic emulsion layer. But such techniques cannot satisfy recent requirements for high speed coating of the photographic emulsion and thinning of the photographic emulsion layer considering the increase of productivity.
On the other hand, since a hydrophilic colloid such as gelatin is contained in the undercoating layer, putrefaction or decomposition takes place due to an influence of microorganisms such as bacteria, yeasts, molds, etc. In order to prevent such putrefaction or decomposition, it is proposed to use a compound of the formula: ##STR1## wherein R.sub.1 ' is hydrogen, an alkyl group or the like; R.sub.2 ', R.sub.3 ' and R.sub.4 ' are independently hydrogen, halogen, an alkyl group or an alkoxy group, in place of a known preservative such as a phenol, a p-hydroxybenzoic acid ester, or the like in the undercoating layer (Japanese Patent Examined Publication No 58-48892, Japanese Patent Unexamined Publication (Laid-Open) No. 61-107343, etc.). Further it is also proposed to use in an undercoating layer a compound of the formula: ##STR2## wherein R.sub.5 ' is hydrogen, a straight- or branched-chain alkyl group, a cyclic alkyl group, an alkenyl group, an aralkyl group, an aryl group, a heterocyclic group, or the like; and R.sub.6 ' and R.sub.7 ' are independently hydrogen, halogen, an alkyl group, a cyclic alkyl group, an aryl group, a cyano group, an alkylthio group, an arylthio group, an alkylsulfoxy group, an alkylsulfonyl group or a heterocyclic group, in place of a known preservative such as a phenol, a p-hydroxybenzoic acid ester, or the like in the undercoating layer (Japanese Patent Unexamined Publication (Laid-Open) Nos. 59-226344, 59-226343, etc.) In addition, it is also proposed to use the above-mentioned two kinds of compounds in the undercoating layer (Japanese Patent Unexamined Publication (Laid-Open) No. 59-142543).
But when these undercoating layers are used, coating properties and adhesive properties against high speed coating of the photographic emulsion layer formed on the undercoating layer becomes insufficient. As mentioned above, when putrefaction and decomposition of a solution for undercoating layer are to be prevented, high coating properties and adhesive properties of the photographic emulsion layer becomes worse. On the other hand, when the coating properties and adhesive properties of the photographic layer are to be improved, the solution for undercoating layer is suffered from putrefaction and decomposition so as to make it impossible to store for a long period of time.